dispersive liquid–liquid microextraction of organophosphorous pesticides using nonhalogenated...

J. Sep. Sci. 2012, 00, 1–6 1

Andreia Cristina HenriquesAlvesMaria Margarida PontesBoavida GoncalvesMaria Manuel SerranoBernardoBenilde Simoes Mendes

Departamento de Ciencias eTecnologia da Biomassa,Faculdade de Ciencias eTecnologia, Universidade Novade Lisboa, Caparica, Portugal

Received March 06, 2012Revised May 27, 2012Accepted May 30, 2012

Short Communication

Dispersive liquid–liquid microextraction oforganophosphorous pesticides usingnonhalogenated solvents

Dispersive liquid–liquid microextraction (DLLME) combined with gas chromatography andmass spectrometry (GC-MS) was applied to the determination of five organophosphorouspesticides (OPPs) in water samples. The analytes included in this study were prophos, di-azinon, chlorpyrifos methyl, fenchlorphos, and chlorpyrifos. The use of nonhalogenatedsolvents (cyclohexane, heptane, and octane) as extraction solvents was investigated usingacetone, acetonitrile, or methanol, as dispersion solvents. The combination of less polardispersion solvents (1-propanol and 2-propanol) and nonhalogenated extraction solventswas also studied in dispersive liquid–liquid microextraction for the first time. Several ex-perimental conditions were tested (nature and volume of extraction solvents, nature andvolume of dispersion solvents, salting-out effect) and the corresponding enrichment factorsand recoveries were evaluated. The best microextraction condition was obtained using 50 �Lof cyclohexane and 0.3 mL of 1-propanol. The detection and quantification limits were in thelow ppt range, with values between 3.3–8.0 ng/L and 11.0–26.6 ng/L, respectively. Relativestandard deviations were between 6.6 and 13.1% for a fortification level of 500 ng/L. Atthe same fortification level, the relative recoveries (RR) of Alvito’s dam water, Judeu’s riverwater, and well water samples were in the range of 50.3–97.1%.

Keywords: Nonhalogenated solvents / Dispersive liquid–liquid microextraction /Gas chromatography-mass spectrometry / Organophosphorous pesticidesDOI 10.1002/jssc.201200241

1 Introduction

Dispersive liquid-liquid microextraction combined with gas-chromatography (DLLME-GC) has been widely and success-fully applied for the determination of different types of pes-ticides including organophosphorous pesticides (OPPs) inaqueous matrices [1–6].

The DLLME-GC applications covering OPPs already pub-lished in the literature are mainly based on the use of halo-genated solvents, particularly, chlorinated solvents. Author’sprevious works [2, 7] demonstrated good extraction efficien-cies and low detection limits were obtained for OPPs extrac-tion from water samples using chloroform and carbon tetra-chloride; however, the replacement of the most commonlyused chlorinated solvents by nonhalogenated organic sol-vents with better environmental advantages and that can pro-vide comparable and reliable results is also being observed inDLLME applications. Some authors presented applications ofDLLME for several analytes with extraction solvents of lower

Correspondence: Andreia Cristina Henriques Alves, Faculdade deCiencias e Tecnologia, Universidade Nova de Lisboa, 2829-516Caparica, PortugalE-mail: [email protected]: 351-21-2948543

Abbreviations: DLLME, dispersive liquid–liquid microextrac-tion; OPPs, organophosphorous pesticides

toxicity, such as alcohols, alkanes, and ionic liquids [8–15].The use of ionic liquids as extraction solvents in DLLMEhas been explored in several aqueous matrixes for pesticideanalysis; Zhou and coworkers [8] developed a temperature-controlled ionic liquid dispersive liquid-phase microextrac-tion for the detection of two OPPs in water samples; He et al.[9] applied the DLLME and used 1-octyl-3-methylimidazoliumhexafluorophosphate for removal of parathion, phoxim, phor-ate, and chlorpyifos from environmental samples; Zhao et al.[10] developed a novel microextraction procedure called, ionicliquid/ionic liquid dispersive liquid–liquid microextraction(IL/IL-DLLME)) for the extraction of pyrethroid pesticidesfrom water samples.

Only a few reports on the application of nonhalogenatedextraction solvents in DLLME can be found in the literature.

Leong et al. [11] studied the extraction of organochlo-ride pesticides in water samples by using DLLME methodbased on solidification of floating organic drop (DLLME-SFO) with undecanol, 1- and 2-dodecanol, and hexadecaneas extraction solvents; Juybari [12] studied DLLME-SFO oforganochloride pesticides testing 1-undecanol as extractionsolvent. Nonhalogenated alcohols or hydrocarbons, with anumber of carbons higher than the most common solvents,are frequently chosen for DLLME-SFO because they presentsolidification temperatures close to 0�C. Still, nonhalogenatedsolvents are less used in DLLME mainly because being lessdense than water, they require additional care in the phase

C© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com

2 A. C. H. Alves et al. J. Sep. Sci. 2012, 00, 1–6

separation operations, to avoid remixing of phases and poorrecoveries.

Farajzadeh et al. [13] proposed the use of nonhalogenatedsolvents such as cyclohexane, toluene, n-hexane, mixture ofxylene isomers, dibutyl ether, and mesytilene in DLLME ofthe OPPs diazinon, fenitrothion, and ethion; these authorsdeveloped a specific extraction device to facilitate the collec-tion of the organic solvent; Chen et al. [14] applied DLLMEto extract carbamate pesticides from water samples usingtoluene, cyclohexane, n-hexane, and octanol as extraction sol-vents;

Moinfar et al. [15] studied DLLME of OPPs (phorate, di-azinon, disolfotane, methyl parathion, sumithion, malathion,fenthion, profenphose, ethion, and phosalone) in tea, select-ing n-hexane as extraction solvent.

The purpose of the present work is the application of theDLLME technique for the extraction of five OPPs (prophos,diazinon, chlorpyrifos methyl, fenchlorphos, and chlorpyri-fos) from water samples using low density/nonhalogenatedorganic solvents.

In this study, cyclohexane, heptane, and octane were usedfor the first time as extraction solvents in DLLME for thisgroup of analytes. Moreover, the optimization of experimen-tal conditions was carried out using nonconventional dis-persion solvents such as 1-propanol and 2-propanol, whichwere tested in combination with nonhalogenated solvents inDLLME (NHS-DLLME). Gas chromatography coupled withmass spectrometry (GC-MS) was used as analytical technique.

2 Materials and methods

2.1 Reagents and standards

The OPPs used in the study (prophos, diazinon, chlorpyrifosmethyl, fenchlorphos, chlorpyrifos) were purchased as a stan-dard mixture (EPA method 622 organophosphorus pesticidesmixture 3, Chemservice, Ref. OPP622–2JM, West Chester,USA) with a concentration of 1000 mg/L in hexane. Thenonhalogenated solvents used were cyclohexane (99% pu-rity) supplied by Lab-scan (Sowinskiego, Poland), heptane(99% purity) obtained from Merck (Darmstadt, Germany),and octane (99% purity) supplied by Koch-Light Laboratory(Cambridge, UK). The dispersion solvents acetone (99% pu-rity), methanol (99.9% purity), and acetonitrile (ACN) (99%purity) were obtained from Lab-scan; 1-propanol (99.5% pu-rity) was purchased from Fluka (Steinheim, Switzerland), and2-propanol (99.8% purity) from Merck. Ultra pure water wasobtained with a Milli-Q purification system (Milipore, Mols-heim, France). The sodium chloride (99.5% purity) was ob-tained from Panreac (Barcelona, Spain). A stock standardsolution of 2 mg/L of pesticide mixture was prepared inmethanol.

The real water samples (Alvito’s dam water, Judeu’s riverwater, and well water) were filtered through a 0.25 �m mem-brane prior to analysis.

2.2 GC-MS analysis

Chromatographic analysis was performed using a Focus gaschromatograph equipped with an auto-sampler AS2000, asplit-splitless injector, a TR-5MS capillary column (30 m ×0.25 mm ID × 0.25 �m film) and a Polaris Q mass spectrom-eter detector (Thermo Scientific, Waltham, USA). The carriergas was helium (99.9999% pure) at 1 mL/min; an aliquot of1 �L from each extract was injected at 260�C in the split-less mode with a splitless time of 1 min and a split flow of30 mL/min; the interface and ion source were kept at 270�Cand 250�C, respectively; the oven temperature program wasas follows: 80�C for 2 min; 15�C/min to 200�C; 4�C/min to220�C, hold for 1 min; 6�C/min up to 240�C; 10�C/min up to250�C, hold for 2 min. The MS system was operated in thefull scan mode with a mass range from m/z 45 to 400. Thechromatographic peaks were identified by comparison of re-tention time and mass spectra of those of authentic standards.Quantification was based in the chromatographic peak area ofsingle ion extracted chromatograms afterwards and ion selec-tion was made using criteria of signal-to-noise maximization.For prophos, the selected ion was 158 (m/z), for diazinon was179 (m/z), for chlorpyrifos methyl was 286 (m/z), for fenchlor-phos was 285 (m/z), and for chlorpyrifos was 314 (m/z).

2.3 NHS-DLLME procedure

The NHS-DLLME procedure consisted in the rapid injec-tion of the mixture of extraction and dispersion solvents into5 mL of ultrapure water fortified with the mixture of OPPs ata concentration of 2 �g/L and placed in a screw cap glass testtube with conic bottom. A cloudy solution, consisting of veryfine droplets of extraction solvent dispersed into the aqueoussample, was formed. The mixture was then centrifuged 5 minat 4000 rpm (centrifuge Mixtasel-BL model from J.P. Selecta,Barcelona, Spain).

The extraction solvents used in the procedure are lighterthan water, providing an organic phase supernatant at the topof the conical vial after the centrifugation. In order to improvethe collection of the organic phase, the maximum of aqueousphase was carefully removed with a syringe equipped witha long and thin needle; a second centrifugation step (5 min,4000 rpm) was performed to enhance the sedimentation ofthe remaining aqueous phase at the bottom of the conicalvial, improving phase’s separation. The supernatant organicphase was collected with an appropriated 10-�L microsyringeand an aliquot of 1 �L was injected into the GC-MS system.

3. Results and discussion

In order to study the efficiency of NHS-DLLME on the re-moval of prophos, diazinon, chlropyrifos methyl, fenchlor-phos, and chlorpyrifos from water samples, several experi-mental parameters like the nature and volume of the extrac-tion solvent, nature and volume of the dispersion solvent,


J. Sep. Sci. 2012, 00, 1–6 Sample Preparation 3

and salting-out effect were optimized. The different condi-tions tested were compared by evaluating the correspondingenrichment factors (EF) and extraction recoveries (R%).

The EF is defined as the ratio between the concentrationof analytes in the supernatant phase (Csup) and the initialconcentration of analyte (C0) in the aqueous phase.

E F = Csup

C0(1)

The extraction recovery (R%) is defined as the percentageof total analyte (n0) that was extracted into the supernatantphase (nsup).

R% = E F × Vsup

Vaq× 100 = nsup

n0× 100 = Csup × Vsup

C0 × Vaq× 100

(2)

where R%, Vsup, and Vaq are the extraction recovery, the vol-ume of supernatant phase, and the volume of aqueous sam-ple, respectively.

To assess the matrix effect on real water samples, dur-ing validation method, the relative recoveries (RR) was deter-mined using the following equation:

RR(%) = Cmeasur ed − Cr eal

Cadded× 100 (3)

where Cmeasured is the concentration of analyte measured afterfortification, Creal is the concentration of analyte measuredbefore fortification, and Cadded is the level of fortification ofthe water samples.

3.1 Optimization of the dispersion conditions and

selection of the best combination of

extraction/dispersion solvents

The extraction solvents chosen to be studied in this work,namely, cyclohexane (density: 0.779 g/mL), heptane (density:0.6838), and octane (density: 0.703 g/mL) less toxic than chlo-rinated solvents, have a good chromatographic behavior andgood ability to dissolve the target compounds. Several dis-persion solvents (acetone, ACN, methanol, 1-propanol, and2-propanol), were selected taking into account their miscibil-ity with water and with the selected extraction solvents. Ina first set of experiments, all possible combinations of ex-traction and dispersion solvents were tested using 100 �L ofextraction solvent, 0.5 mL of dispersion solvent, and 5 mL ofwater fortified with the OPPs mixture at a concentration of 2�g/L. Combining cyclohexane as extraction solvent with allthe different dispersion solvents, higher enrichment factors(EF) (between 105 and 157) and recoveries (higher than 75%for all the analytes) were obtained using 1-propanol as dis-persion solvent (Fig. 1); for heptane as extraction solvent, thebest result concerning analytes partition was obtained withmethanol, presenting EFs in the range of 112–189 and recov-eries between 51 and 70%; with octane the best EFs (107–156)

Figure 1. Enrichment factors and recoveries of OPPs in DLLMEprocedure for cyclohexane/1-propanol. DLLME conditions: watersample volume, 5 mL; extraction solvent (cyclohexane) volume,100 �L; dispersion solvent (1-propanol) volume, 0.5 mL; spike of2 �g/L of OPPs.

Figure 2. Optimization of cyclohexane volume. DLLME condi-tions: water sample volume, 5 mL; extraction solvent (cyclohex-ane) volume, 40, 50, 60, 100 �L; dispersion solvent (1-propanol)volume, 0.5 mL; spike of 2 �g/L of OPPs.

and recoveries (133–175%) were obtained for the combinationwith dispersive solvent ACN. The system heptane/methanolpresented the higher EFs however the organic volume col-lected was not always reproducible and recoveries are belowthan 70%, which is a drawback. For the octane/ACN system,recoveries were far above 100% and the supernatant volumecollected was around 60 �L, which suggests that completephase separation might not be achieved. In face of these re-sults, the system cyclohexane/1-propanol was selected as thebest combination of extraction/dispersion solvents for furtheroptimization.

3.2 Cyclohexane volume optimization

Several cyclohexane volumes were tested (40, 50, 60, and 100�L) in combination with 0.5 mL of 1-propanol and 5 mL ofwater fortified with OPPs. The results presented in Fig. 2show that the maximum EFs were obtained using 50–60�L of cyclohexane. The organic phase volume collectedranged between 13 and 10 �L, respectively. However, higher



Figure 3. Salting-out effect. DLLME conditions: water sample vol-ume, 5 mL; extraction solvent (cyclohexane) volume, 50 �L; dis-persion solvent (1-propanol) volume, 0.5 mL; 10% NaCl (w/v);spike of 2 �g/L of OPPs.

recoveries (between 50 and 76%) were obtained using 50 �Lof cyclohexane.

3.3 Salting-out effect

The salting-out effect is an interesting parameter to study inDLLME, especially when using nonhalogenated solvents asextraction solvents, since the increase of salt concentration inthe aqueous phase may favor the phase separation by increas-ing the density of water phase. In this study, the salting-outeffect was investigated using a NaCl solution with a concen-tration of 10% (w/v), the selected cyclohexane volume (50 �L),and 0.5 mL of 1-propanol. This salt concentration was chosentaking into account other literature reports [12,13], where themaximum of salt concentration added to aqueous phase wasaround 10–20% (w/v). According to Fig. 3, the EFs (71–128)and recoveries (20–36%) obtained using 10% NaCl in aque-ous solution were worse than without salt addition, showingthat the increase of the ionic strength of aqueous phase isnot advantageous to analyte’s partition. These results wereaccording to Farajzadeh and coworkers study [13], where theaddition of salt to the aqueous phase didn’t promote a betterextraction efficiency of OPPs from water samples.

Thus, the conditions chosen were 50 �L of cyclohexaneand no salt addition in the aqueous phase.

3.4 Dispersion solvent (1-propanol) volume

optimization

The dispersion solvent volume (1-propanol) was optimizedperforming tests with 0.3, 0.4, 0.5, 0.6, and 0.7 mL. HigherEFs were obtained for 0.3 and 0.4 mL of 1-propanol(Fig. 4). When using 1-propanol volumes above 0.4 mL, phaseseparation decreases resulting in lower extraction efficiency,less defined interface between aqueous and organic phases,and irreproducibility of the collected volumes. Therefore, theselected dispersion volume was 0.3 mL because it provides

Figure 4. Dispersion volume (1-propanol) optimization. DLLMEconditions: water sample volume, 5 mL; extraction solvent (cyclo-hexane) volume, 50 �L; dispersion solvent (1-propanol) volume,0.3, 0.4, 0.5, 0.6, 0.7 mL; spike of 2 �g/L of OPPs.

Table 1. Detection limits, quantification limits, and relative stan-dard deviation values of proposed method for the fiveOPPs

Pesticide LODa) LOQb) RSDc)

(ng/L) (ng/L) (%), n = 4

Prophos 8.0 26.6 13.1Diazinon 4.5 15.1 12.5Chlorpyrifos methyl 4.4 14.7 9.8Fenchlorphos 3.3 11.0 6.6Chlorpyrifos 4.7 15.7 6.6

a)LOD, limit of detection based on signal-to-noise ratio of 3 at aconcentration level of 500 ng/L;b)LOQ, limit of quantification based on signal-to-noise ratio of 10at a concentration level of 500 ng/L;c)RSD, residual standard deviation at concentration level of 500ng/L for each OPP.

a good EF and reproducible organic phase volumes (around20 �L) .

3.5 Evaluation of analytical performance of

NHS-DLLME method

The evaluation of analytical performance of NHS-DLLME wasachieved by determining the detection limits and repeatabilityat 500 ng/L for the five OPPs (Table 1), using the optimizedNHS-DLLME conditions. The LODs were determined basedon a signal-to-noise ratio of 3 and ranged from 3.3 to 8.0 ng/L;the LOQs were determined based on a signal-to-noise ratio of10 and ranged from 11.0 to 26.6 ng/L. Thus, the lower analyt-ical limits show good applicability of the optimized microex-traction method for OPPs removal from aqueous samples.Furthermore, the analytical performance of the developedmethod suggests that it can be applied in surface, ground,and drinking water samples, since both detection and quan-tification limits obtained were far below the maximum im-posed limits defined in the EU Council Directives 98/83/EC


J. Sep. Sci. 2012, 00, 1–6 Sample Preparation 5

Table 2. Relative recoveries (RR) and RSD values of OPPs in realwater samples

OPPs RRa) (%) ± SDb) (n = 2)

Alvito’s dam Judeu’s river Wellwater water water

Prophos 50.3 ± 3.6 91.7 ± 22.6 66.0 ± 7.3Diazinon 53.1 ± 9.2 83.1 ± 2.7 84.7 ± 17.0Chlorpyrifos methyl 89.0 ± 14.4 84.2 ± 31.5 82.7 ± 9.4Fenchlorphos 65.2 ± 11.5 79.6 ± 18.2 72.1 ± 17.0Chlorpyrifos 66.4 ± 2.0 75.6 ± 20.2 91.0 ± 8.3

a)RR, relative recovery;b)SD, standard deviation.

and 2006/118/EC, concerning the pesticide’s concentrationin drinking and ground waters, respectively. [15, 16]

The repeatability of the developed method was evaluatedby analyzing four replicates at a concentration level of 500ng/L. The NHS-DLLME method showed good precision withrelative standard deviations (RSD) between 13.1 and 6.6% forthe five OPPs.

3.6 Real water sample analysis

The application of NHS-DLLME method was tested in realsurface and groundwater samples (Judeu’s river water, wellwater, and Alvito’s dam water). Each sample was spiked with

the target analytes at a concentration level of 500 ng/L. TheRR after fortification of real water samples were in the rangeof 50.3–89.0% for dam water, 75.6–91.7% for river water, and66–91.0% for well water (Table 2).

These results indicate that the matrix effect of the realwater samples was minimal in NHS-DLLME method, repre-senting good recovery of OPPs in spiked samples.

The slight decrease of RR of some OPPs may be dueto the presence of higher amount of organic matter in damwater. Yet, these results demonstrate that the proposed NHS-DLLME method has good accuracy for the detection of OPPsin real surface and groundwater samples.

3.7 Comparison the NHS-DLLME method with other

methods

The analytical performance of the developed method wascompared with other microextraction methods [2, 8, 9, 12, 13]for OPPs removal from water samples (Table 3). The analyti-cal limits, i.e. the detection (3.3–8.0 ng/L) and quantification(11.0–26.6 ng/L) limits of developed NHS-DLLME methodare far below the maximum imposed limit (100 ng/L) forpesticides [16, 17]. Comparing to our previous work [2], theOPPs DLLME was performed using chloroform as extractionsolvent and, higher EFs (above 200) were obtained; in thiswork, however, comparable LODs were determined for theseOPPs using less toxic organic solvents at low volume. Thisfact is considered an improvement in the microextraction

Table 3. Comparison of NHS-DLLME-GC-MS with other methods for determination of OPPs in water samples

Method Analytes LOD (ng/L) EFs Vexta) (�L) Extraction solvent Reference

NH-DLLME-GC-MS Prophos 8.0 100 50 Cyclohexane This studyDiazinon 4.5 154Chlorpyrifos methyl 4.4 168Fenchlorphos 3.3 176Chlorpyrifos 4.7 179

DLLME-GC-MS Prophos 5.1 319 50 Chloroform [2]Diazinon 3.9 259Chlorpyrifos methyl 1.5 257Fenchlorphos 1.9 249Chlorpyrifos 2.5 235

DLLME-GC-MS Diazinon 3 112 100 Cyclohexane [8]Fenitrothion 3 140Ethion 3 120

DLLME-SFO-GC-ECD Endosulfan 50 905 Undecanol [12]Butachlor 6 915 15Dichlorvos 8 802

IL-DLLME-HPLC-UV Methyl parathion 170 50 50 [C6MIM][PF6] [13]Proxim 290 50

IL-DLLME-HPLC-UV Parathion 500 >200 35 [C8MIM][PF6] [14]Proxim 100Phorate 2500Chlorpyrifos 5000

a)Vext, extraction solvent volume.



field and more specifically for OPPs trace analysis. The LODsobtained in this work are significantly lower than the LODsobtained by Zhou et al. [8] and He et al. [9] using ionic liq-uids in an IL-DLLME-HPLC-UV application. Moreover, theLODs and EFs obtained in this work are comparable to theones obtained by Farajzadeh et al. [13], though higher cyclo-hexane volume (100 �L) was required for DLLME-GC-MS.In Juybari et al. [12] work, other OPPs were tested, how-ever the LODs presented in this work are slightly lowerthan the ones determined using an alcohol as extractionsolvent.

Still, the microextraction methods associated to gas chro-matography analysis [12, 13] revealed higher analytical per-formance for OPPs routine analysis, than microextractionmethods associated to liquid chromatography.

In this study, the development of a new DLLME methodinvolving less toxic organic solvents such as nonhalogenatedsolvents, demonstrated a good practical applicability ofDLLME in real water analysis.

4 Concluding remarks

In this study, the development of new DLLME method forthe trace analyses of five OPPs in water samples consistedin the use of less toxic organic extraction solvents, such asnonhalogenated solvents and their combination with conven-tional and nonconventional dispersion solvents (1-propanoland 2-propanol). The best extraction/dispersion solvent com-bination was attained with cyclohexane/1-propanol. The de-tection and quantification limits obtained for OPPs were farbelow than the imposed limit (100 ng/L) for drinking andground water samples [16, 17], still higher recoveries, EFs,and good repeatability were considered. The practical appli-cability of the method was tested in three real water samples(river, well, and dam waters) and high RR (all above 50%)were obtained.

The authors wish to thank the support of Dr. Marco Gomesda Silva in the analytical analysis of real water samples.

The authors have declared no conflict of interest.

5 References

[1] Berijani, S., Assadi, Y., Anbia, M., Hosseini, M. R. M.,Aghaee, E., J. Chromatogr. A 2006, 1123, 1–9.

[2] Alves, A., Goncalves, M., Bernardo, M., Mendes, B., J.Sep. Sci. 2011, 34, 1326–1332.

[3] Xiong, J., Hu, B., J. Chromatogr. A 2008, 1193, 7–18.

[4] Zhao, R. S., Diao, C. P., Wang, X., Jiang, T., Yuan, J. P.,Anal. Bioanal. Chem. 2008, 391, 2915–2921.

[5] Xiao-Huan, Z., Chun, W., Shu-Tao, Xin, G., Zhi, Z., Chin,W., J. Anal. Chem. 2008, 36, 765.

[6] Rezaee, M., Yamini, Y., Faraji, M., J. Chromatogr. A 2010,1217, 2342–2357.

[7] Alves, A., Goncalves, M., Bernardo, M., Mendes, B., J.Sep. Sci. 2011, 34, 2475–2481.

[8] Zhou, Q., Bai, H., Xie, G., Xiao, J., J. Chromatogr. A 2008,1188, 148–153.

[9] He, L., Luo, X., Xie, H., Wang, C., Jiang, X., Lu, K., Anal.Chim. Acta 2009, 655, 52–59.

[10] Zhao, R. S., Wang, X., Li, F. W., Wang, S. S, Zhang, L. L.,Cheng, C. G., J. Sep. Sci 2011, 34, 830–836.

[11] Leong, M., Huang, S., J. Chromatogr. A 2009, 1216, 7645–7650.

[12] Juybari, M. B., Mehdinia, A., Jabbari, A., Yamini, Y., Chro-matogr. Res. Int. 2011, 2011, 1–8.

[13] Farajzadeh, M. A., Seyedi, S. E., Shalamzari, M. S.,Bamorowat, M., J. Sep. Sci. 2009, 32, 3191–3200.

[14] Chen, H., Chen, R., Li, S., J. Chromatogr. A 2010, 1217,1244–1248.

[15] Moinfar, S., Hosseini, M. R. M., J. Hazard. Mater. 2009,169, 907–911.

[16] The Council of European Union, Council Directive98/83/EC of 3 November 1998 on the quality of waterintended for human consumption, Brussels, Belgium1998.

[17] The Council of European Union, Council Directive2006/118/EC of 12 December 2006 on the protection ofgroundwater against pollution and deterioration, Stras-bourg, France 2006.


dispersive liquid–liquid microextraction of organophosphorous pesticides using nonhalogenated...

Documents